Surface tension of liquid Ti with adsorbed oxygen and its prediction

Kurzfassung

Surface tensions of electromagnetically levitated liquid Ti-samples were measured under the influence of oxygen. The partial pressure of oxygen is controlled by means of yttria-stabilized zirconia tubes as well as Ar/H2/H2O buffer gas mixtures. In addition, Ti-O samples were prepared by adding different amounts of TiO2 powder to pure Ti. No significant dependence of the surface tension on the applied oxygen partial pressure was found for the samples processed. However, the surface tension was found to strongly depend on the bulk oxygen mole fraction determined by chemical analysis. From some experiments a small time dependence of the surface tension became evident. The observed dependencies of the surface tension on oxygen mole fraction as well as on time could be described by the model developed in the present work. It is based on adsorption/desorption rate equations and the surface tension is calculated from the ideal Butler equation. Non-ideal interactions between oxygen and titanium are taken into account. It is generally observed that, due to the strong attractive interaction between Ti and oxygen, the surface tension of Ti is much less sensitive to the presence of oxygen than the surface tension of other metallic systems.